The previous version was very innefficient due to the benchmarks used
to optimize it having a bug. This version always allocates a new
slice, but is O(n).
This switches compactions to use type values (FloatValues) from the
generic Values type. It avoids a bunch of allocations where each value
much be converted from a specific type to an interface{}.
Still seeing the panic that switching this logic around was supposed
to fix. We now delete the bulk of data outside of the fields lock
and then again, under the write lock, to ensure that the field mapping
is accurate. We don't do the full delete under the lock because it
can block writes and queries that require a read lock.
If blocks containing overlapping ranges of time where partially
recombined, it was possible for the some points to get dropped
during compactions. This occurred because the window of time of
the points we need to merge did not account for the partial blocks
created from a prior merge.
Fixes#8084
There is a race where the field type can be deleted while a new type
is written and during a query. When this happens, an iterator for
the new type is created but old data make still exist in the cache
for TSM files causing a panic.
Under high query load, a race exists in the cache and the WAL. Since
writes currently hit the cache first, they are availble for query before
they hit the WAL. If the WAL is writing and accessign the Value slice
at the same time that a query is run that needs to dedup the same slice,
a race occurs.
To fix this, the cache now just copies the values instead of storing the
slice passed in. Another way to fix this might be to have the writes go
to the wal before the cache. I think the latter would be better, but it
introduces some larger write path issues that we'd need to also address.
e.g. if the cache was full, writes to the WAL would need to be rejected
to avoid filling the disk.
Copying the slice in the cache is simpler for now and does not appear to
dramatically affect performance.
Previously, tags had a `shouldCopy` flag to indicate if those tags
referenced an underlying buffer and should be copied to allow GC.
Unfortunately, this prevented tags from being copied that were
created and referenced the mmap which caused segfaults.
This change removes the `shouldCopy` flag and replaces it with a
`forceCopy` argument in `CreateSeriesIfNotExists()`. This allows
the write path to indicate that tags must be cloned on insert.
They rebased a revision we were previously relying upon that allowed us
to use the vanity name so we are reverting back to an older version with
the old import path.
The order of series keys is in ascending alphabetical order, not
descending alphabetical order, when it is ordered by descending time.
This fixes the ordering so points are returned in descending order. The
emitter also had the conditions for choosing which iterator to use in
the wrong direction (which only affects aggregates with `FILL(none)`).
This fixes LIMIT and OFFSET when they are used in a subquery where the
grouping of the inner query is different than the grouping of the outer
query. When organizing tag sets, the grouping of the outer query is
used so the final result is in the correct order. But, unfortunately,
the optimization incorrectly limited the number of points based on the
grouping in the outer query rather than the grouping in the inner query.
The ideal solution would be to use the outer grouping to further
organize it by the grouping for the inner subquery, but that's more
difficult to do at the moment. As an easier fix, the query engine now
limits the output of each series. This may result in these types of
queries being slower in some situations like this one:
SELECT mean(value) FROM (SELECT value FROM cpu GROUP BY host LIMIT 1)
This will be slower in a situation where the `cpu` measurement has a
high cardinality and many different tags.
This also fixes `last()` and `first()` when they are used in a subquery
because those functions use `LIMIT 1` as an internal optimization.
Every write to the WAL current runs and fsync before returning. When
there are lot of concurrent writes, this can cause the WAL to bottleneck
write throughput since fsyncs are very expensive.
This changes the writeToLog to fsync on an interval to allow multiple fsyncs
calls to be batched up into one. The writeToLog behavior is the same in that
it won't return until an fsync has been performed.
I ran into an issue where the cache snapshotting seemed to stop
completely causing the cache to fill up and never recover. I believe
this is due to the the Timer being reused incorrectly. Instead,
use a Ticker that will fire more regularly and not require the resetting
logic (which was wrong).
The memory stats as well as the size of the cache were not accurate.
There was also a problem where the cache size would be increased
optimisitically, but if the cache size limit was hit, it would not
be decreased. This would cause the cache size to grow without
bounds with every failed write.
The CacheKeyIterator (used for snapshot compactions), iterated over
each key and serially encoded the values for that key as the TSM
file is written. With many series, this can be slow and will only
use 1 CPU core even if more are available.
This changes it so that the key space is split amongst a number of
goroutines that start encoding all keys in parallel to improve
throughput.
This simplifies the cache.Snapshot func to swap the hot cache to
the snapshot cache instead of copy and appending entries. This
reduces the amount of time the cache is write locked which should
reduce cache contention for the read only code paths.
Also, fix the `Iterators.Merge(IteratorOptions)` function so it consults
the `Ordered` attribute to determine which iterator it should use to
merge the input iterators.
The backup command can fail if a snapshot is running which silently
closes the connection. This causes the backup shard command to continue
on as if nothing failed.
This adds query syntax support for subqueries and adds support to the
query engine to execute queries on subqueries.
Subqueries act as a source for another query. It is the equivalent of
writing the results of a query to a temporary database, executing
a query on that temporary database, and then deleting the database
(except this is all performed in-memory).
The syntax is like this:
SELECT sum(derivative) FROM (SELECT derivative(mean(value)) FROM cpu GROUP BY *)
This will execute derivative and then sum the result of those derivatives.
Another example:
SELECT max(min) FROM (SELECT min(value) FROM cpu GROUP BY host)
This would let you find the maximum minimum value of each host.
There is complete freedom to mix subqueries with auxiliary fields. The only
caveat is that the following two queries:
SELECT mean(value) FROM cpu
SELECT mean(value) FROM (SELECT value FROM cpu)
Have different performance characteristics. The first will calculate
`mean(value)` at the shard level and will be faster, especially when it comes to
clustered setups. The second will process the mean at the top level and will not
include that optimization.
The previous implementation was susceptible to a race condition (of
correctness) since c.decreaseSize is called without a lock in
(*Cache).WriteMulti.
There were already tests which asserted the correctness of the result of
decreaseSize, so no tests were added or modified.
Jason Wilder
Jason Wilder
Ben Johnson
Mark Rushakoff
Jonathan A. Sternberg
Edd Robinson
Joe LeGasse
Mark Rushakoff
Cory LaNou